Make the mint oil by adding all of the ingredients in a good processor and blitzing for 1-2 minutes until smooth. Store in the fridge until ready to use.
Add the potatoes, halloumi, aubergine and tomatoes to the mint oil. Mix well to ensure everything is evenly coated.
Strip the base rosemary leaves from each stem, leaving the top 4cm of each with leaves.
Thread alternate potato, halloumi, aubergine and tomatoes along each stem and continue until everything is used up.
Preheat the barbecue or grill. Cover the leave tops of the rosemary skewers with a sheet of tin foil to prevent them burning.
Grill or barbecue the skewers over a medium heat for about 10-15 minutes, turning regularly until the potatoes are cooked through and the vegetables are golden. Baste occasionally with the mint oil.
Serve with a drizzle of the remaining mint oil.